The present invention relates to power supply converter circuits, and in particular to converter circuits known as resonant converters, and more particularly to such converters for powering gas discharge lamps, e.g., fluorescent lamps.
Typical existing converter solutions include a power factor correction (PFC) stage for producing a sinusoidal input current and a regulated DC bus voltage, followed by a resonant mode output stage necessary for converting the DC bus voltage to the desired output voltage level. See FIG. 1.
The PFC stage is typically realized with a boost-type converter and requires a high voltage switch, an inductor, a diode, a high voltage DC bus capacitor, and a PFC control circuit. The resonant mode output stage is typically realized with a half-bridge driven resonant load and requires two high voltage switches, a resonant inductor, a resonant capacitor, a DC-blocking capacitor and a ballast control circuit.
In a traditional half-bridge ballast output stage configuration, as shown in FIG. 2, the top switch of the half-bridge, M1, and the top of the DC bus capacitor, Cbus, are connected together at a single node. The power factor controller, comprised of Lpfc, Mpfc, Dpfc and a PFC control chip (not shown), must first charge Cbus and then Cbus supplies the half-bridge resonant converter the entire time.